1. Field of the Invention
The present invention generally relates to a casting method for manufacturing a golf club head and, more particularly, to a casting method for manufacturing a golf club head having an embedded heterogeneous material different from the cast material.
2. Description of the Related Art
In order to meet the needs of a low and deep gravity center, vibration resistance and a comfortable hitting feeling, heterogeneous material different from cast material is currently used in several kinds of golf club heads. By embedding the heterogeneous material into the golf club head, the gravity center of the golf club head and the feeling of the user hitting a golf ball can be adjusted. The heterogeneous material is usually used in the toe, the sole, the heel, the back, the hosel or the striking face of the body of the golf club heads.
Current golf club heads are manufactured by using a high frequency induction furnace to rapidly melt the cast materials in the atmosphere, followed by removing slag and gases in the molten metal by slagging and refinery, Static gravity pouring is then carried out. For maintaining the flowability of the molten metal, the shell mold should be preheated at a high temperature before the pouring process. However, when manufacturing the golf club head with the heterogeneous material, the heterogeneous material in the shell mold is apt to react with oxygen in the air, forming an oxide layer on the surface of the heterogeneous material. Therefore, the coupling strength between the cast material and the heterogeneous material is decreased. Moreover, the heterogeneous material has a thermal expansion coefficient different from the cast material, such that the high temperature used to heat the shell mold during the gravity pouring process often easily causes loosening between the cast material and the heterogeneous material after cooling.
In addition, the static gravity pouring requires additional cast material to maintain the pressing effect of the molten metal and to improve the yield rate of the golf club heads. However, the use of additional cast material and energy for melting the additional cast material results in a higher cost.
Furthermore, if the cast material contains active metals, rigorous oxidation of the active metals may easily occur during the smelting process of the cast material. This not only increases the difficulty in melting but also easily causes oxidative fire cracks due to the reaction with air during the pouring process. As a result, appearance defects, such as sesame dot defects and black bean defects, are apt to be formed on the cast products of the golf club heads. In the worse situations, the reactive gas forms a large number of slag holes or blowholes in the cast products of the golf club heads and, thus, adversely affects the tensile strength of the golf club heads. Moreover, rigorous oxidation also reduces the flowability of the molten metal in the shell mold, leading to a reduced yield rate of the cast products of the golf club heads due to insufficient pouring or resulting in gaps in the cast products of the golf club heads due to cold shut. The tensile strength of the cast products of the golf club heads is also adversely affected. As a result, the yield rate of the cast products of the golf club heads with active metals manufactured by static gravity pouring in the atmosphere is severely decreased.
In light of this, it is necessary to improve the conventional method for manufacturing a golf club head.